Knitted wire carriers are well known. Basically, such carriers comprise a continuous wire weft formed into a zig-zag formation with substantially parallel limbs interconnected by connecting regions at each end of the limbs onto which weft is knitted a plurality of warp threads. These warp threads can be of small wire, a synthetic resin or a natural fiber.
Such a wire carrier is widely used, mainly as a reinforcing frame for coated polymeric products, especially extrusion coated products, such as weather seals on motor vehicles. During manufacture of the seals, the carrier is passed through an extruder and is thus subjected to stresses and temperatures which can cause the warp threads to drift laterally, stretch longitudinally and degenerate both physically and chemically. This can result, for example, in breakage of the warps and distortion of the wire carrier which affects the extrusion process and leads to reduced quality and performance of the corresponding seal. In forming and extrusion processes drifting of the warp threads can cause air bubbles and exposure of the wire in the final weather seal. There has long been a need to develop a stable knitted wire carrier for extruded and molded polymeric products which overcomes these problems and many attempts have been made without complete success.
One attempt to solve the problem of lateral warp shifting formed adjacent zig-zag loops into a propeller or banana shape, but this is difficult to control, and has little effect on preventing lateral warp drifting.
In another attempt to solve the problem, Beck et al, EP Application No. 0175818, have suggested a knitted wire carrier with knotted junctions between the warp threads and the wire weft. Both the warp threads and the wire weft comprise polymeric or polymeric coated material and the polymeric material of the warp and the weft must both be melted to form a weld or fusion at the crossover points. This structure suffers from several disadvantages. It is difficult and expensive to provide either a polymer-coated wire weft, or the combination of an uncoated wire weft with a polymeric material which is fed to the knitting machine with the wire. Furthermore the use of polymeric meltable materials in both the warp and weft increases the cost of the wire carrier. These disadvantages increased the costs enough that it could not be used commercially.
EP 0384613 discloses a knitted wire carrier in which stitched warp threads comprise two threads of polymeric material having different melting points such that when the melting point of the lower melting thread is exceeded the melted thread causes the other thread to be attached to the wire weft. This structure allows single strands of warp thread plied with a meltable filament to be bonded to the wire carrier wherever they are knitted.
In an attempt to prevent movement and fraying at the edges of cut selvages of fabric woven with inorganic materials, such as glass fiber or metallic wire, U.S. Pat. No. 35 15623 discloses a woven carrier for reinforcing roofing and wrapping papers in which a thermoplastic strand is incorporated with one or more of the warp strands adjacent to the cut. On heating, the thermoplastic strand melts and collapses toward the crossover points to hold the strands in place. This deposition of the melted strand at the crossover points could produce an uneven, raised finish which is not desirable in a weather seal as it could result in air bubbles and exposed wire. Although the thermoplastic strand can cause a narrowing of the space between the warp strands there is no suggestion of contact between, or bonding together of adjacent warp strands.
None of the above described constructions provides an entirely satisfactory structure for a knitted wire carder having polymeric warp threads attached to a wire support for use in a weather seal. A knitted wire carrier which allows close grouping and bonding of adjacent warp threads in varying widths at selected positions on the wire affords a strong, stable wire carder and greater control of the subsequent product.
Accordingly, it is an object of this invention to provide a strong, stable wire carrier essentially free of warp drift by knitting warp threads on a wire support and laying-in a meltable filament into groups of adjacent warp threads.
It is another object of this invention to provide such a wire carrier which allows close grouping of adjacent warp threads at selected positions on the wire.
It is another object of this invention to provide such a wire carrier which allows bonding of different numbers of adjacent warp threads to the wire.
It is another object of this invention to provide such a wire carder which allows bonding of different numbers of adjacent warp threads to each other.
It is yet another object of this invention to provide a method for constructing such a wire carder using existing knitters without the need for substantial modification.
It is yet another object of this invention to provide a wire carder which allows greater control of the profile, appearance, quality and performance of a weather seal formed from the wire carrier.